Catalytic conversion of methane and natural gas to condensable hydrocarbons

ABSTRACT

Catalytic processes are taught for oxidative chemical conversion of gaseous reactants comprising methane, natural gas or other gaseous compounds combined with air or oxygen to products and catalytic methanation of resulting oxidized products comprising alcohols, aldehydes, ketones, glycol ethers and aldols to condensable hydrocarbons using methane, natural gas or other gaseous hydrocarbons. Gaseous reactants including methane, ethane, propane, oxides of carbon, unsaturated compounds and other organic compounds with conversion to condensable hydrocarbons by this catalytic process. The catalysts are based on di-metal, tri-metal and/or poly-metal backbone or molecular string type compounds of transition metals, comprising titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, molybdenum, ruthenium, rhodium, palladium, silver, hafnium, tantalum, tungsten, rhenium, osmium, iridium, platinum, gold and combinations thereof in conjunction with a non-fluoride magnesium halide.

BACKGROUND

1. Field of Invention

This invention relates to catalytic conversion of carbon containing gaseous compounds including methane, natural gas and other gaseous carbon containing compounds to condensable alkanes and alkenes with catalysts based on molecular strings of di-, tri- and/or poly-groups of bonded transition metal complexes in conjunction with a non-fluoride salt comprising magnesium halides.

2. Description of Prior Art

A number of catalytic chemical processes have been reported for partial oxidation of methane. Methanol is often a product of partial oxidation while formaldehyde may also be produced. These processes specifically exclude conversion of synthesis gas to products since they are not products of methane conversion, rather employ hydrogen as a reductive co-reactant. Controlled air oxidation of certain gaseous hydrocarbons may produce small amounts of aldehydes, however such processes have not been identified as economically viable. Formaldehyde formation by direct air oxidation of methane has not previously been productive.

There are a limited number of catalytic reactions described in the scientific and patent literature for conversion of methane to a range of low concentration products from carbon oxides to polymeric residues that include small amounts of formaldehyde. Methanol has been formed by dissolving methane in a solvent using a RuLO catalyst at 20° C. to 60° C., 5 to 20 atmospheres pressure, in 30 minutes to 30 hours in the presence of controlled amounts of air as taught by U.S. Pat. No. 5,347,057, issued Sep. 13, 1994. U.S. Pat. No. 5,336,826, issued Aug. 9, 1994, teaches a process for the selective oxidation of methane to higher molecular weight hydrocarbons in the vapor phase in a quartz reactor at 600° C. to 800° C. over Li doped catalyst of niobia, zirconia, thoria, tantala or boria. Less selective chemistry may oxidize methane to carbon oxides and low concentrations of by products.

Catalytic reduction of aldehydes, alcohols and other compounds to hydrocarbons has been conducted previously with the nearly exclusive use of hydrogen gas. Hydrogen gas is commonly manufactured from hydrocarbons such as methane with the loss of carbon or from carbon and water at high temperature by a steam reformation process. Production of hydrogen by these processes is expensive but may be less expensive than the electrolytic process. Natural gas and methane are available renewable resources, although natural gas is presently taken from underground wells.

A number of other chemical reaction paths have previously been investigated for use of methane as a reactant including controlled oxidation of methane to alcohols and aldehydes, chlorination of methane to make reactive intermediates and application of methane sulfonic acid to produce methanated compounds. Chlorination of methane has also been conducted, however formation of higher molecular weight hydrocarbons may be conducted with formation of metal chlorides, hydrogen chloride or other chlorinated compounds resulting in a loss of chlorine, its acids or its salts. In the chemical industry, methane has been a raw material for the manufacture of methanol (CH₃OH), formaldehyde (CH₂O), nitromethane (CH₃NO₂), chloroform (CH₃Cl), carbon tetrachloride (CCl₄), and some freons. The reactions of methane with chlorine and fluorine are triggered by light. When exposed to bright visible light, mixtures of methane with chlorine or fluorine react explosively. Application of methane sulfonic acid as a viable reactant is of limited use and produces sulfuric acid as a by product. The aforementioned methane reaction routes are expensive, produce significant by products and hazardous waste residues.

Reaction of methane with other organic compounds has long been sought as a method of obviating the need for hydrogen gas but such reactions have not been accomplished in economically viable processes. Current industrial chemical methane processes generates synthesis gas, halocarbons, hydrogen cyanide, acetylene, carbon disulfide and carbon but reaction efficiencies for production of saturated hydrocarbons are quite low and may be conducted only in the presence of hydrogen gas.

The present application teaches use of methane and natural gas as direct reducing agents for carbon oxides, formaldehyde and other oxidized low carbon number gaseous compounds resulting in formation of condensable hydrocarbons using selected catalysts. For example, catalytic methane reduction or methanation of formaldehyde to condensable hydrocarbons proceeds readily at elevated temperatures and modest pressure. Typical products include ethylene, propane and similar products.

It is an object of this invention, therefore, to provide a molecular string type transition metal catalytic process for methanation of partially oxidized compounds resulting in formation of condensable gaseous hydrocarbons.

It is another object of this invention to provide a molecular string type transition metal catalytic process for conversion of methane and natural gas to condensable hydrocarbons.

It is still another object of this invention to provide molecular string type transition metal catalysts in conjunction with a non-fluorinated magnesium halide for direct production of condensable hydrocarbons including ethylene, propane and other hydrocarbons.

Other objects of this invention will be apparent from the detailed description thereof which follows, and from the claims.

SUMMARY OF THE INVENTION

This invention describes catalytic oxidative chemical conversion of gaseous reactants including methane, natural gas or other gaseous hydrocarbons combined with air or oxygen to products and subsequent catalytic methanation of resulting oxidized products comprising alcohols, aldehydes and other carbon compounds to condensable hydrocarbons using methane, natural gas or other gaseous hydrocarbon reducing agents using selected members of a family of transition metal catalysts, based on a di-metal, tri-metal and/or poly-metal backbone or string type compounds in conjunction with a non-fluorinated magnesium halide promoter. These catalysts have been effectively demonstrated to be active for formation of condensable hydrocarbons.

DETAILED DESCRIPTION OF THE INVENTION

A process is taught for catalytic oxidative chemical conversion of gaseous reactants comprising methane, natural gas or other gaseous hydrocarbons combined with air or oxygen to products and catalytic methanation of resulting oxidized products comprising alcohols, aldehydes, ketones, glycol ethers and aldols to condensable hydrocarbons using methane, natural gas or other gaseous hydrocarbon reducing agents, catalysts being made from di-metal, tri-metal and/or poly-metal backbone or molecular string type compounds of transition metals, comprising titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zirconium, niobium, molybdenum, ruthenium, rhodium, palladium, silver, hafnium, tantalum, tungsten, rhenium, osmium, iridium, platinum, gold and combinations thereof in conjunction with a promoter comprising magnesium salt comprising magnesium chloride, bromide or iodide. No hydrogen gas, strong oxidizing acids such as sulfuric or fuming sulfuric acid or electromagnetic energy of any type including electric current, microwaves, x-rays or ionizing radiation were employed. Catalysts, such as [vanadium]₂, [manganese]₂ or [cobalt]₂ type compounds, for which the transition metals and directly attached atoms possess C_(4v), D_(4h) or D_(2d) point group symmetry. These catalysts have been designed based on a formal theory of catalysis, and the catalysts have been produced, and tested to prove their activity. The theory of catalysis rests upon a requirement that a catalyst possess a single metal atom or a molecular string such that transitions from one molecular electronic configuration to another be barrier free so reactants may proceed freely to products as driven by thermodynamic considerations. Catalysts effective for partial oxidation of methane, natural gas or other gaseous hydrocarbons to aldehydes and other products can be made from mono-metal, di-metal, tri-metal and/or poly-metal backbone or molecular string type compounds of the transition metals comprising titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zirconium, niobium, molybdenum, ruthenium, rhodium, palladium, silver, hafnium, tantalum, tungsten, rhenium, osmium, iridium, platinum, gold and/or combinations thereof. These catalysts are made in the absence of oxygen so as to produce compounds wherein the oxidation state of the transition metal is low, typically monovalent or divalent although trivalent metal catalysts may also be effective. Anions employed for these catalysts comprise fluoride, chloride, bromide, iodide, cyanide, sulfate, phosphate, borate, oxide, hydroxide, oxalate, acetate, organic chelating agents and/or other groups. Mixed transition metal compounds have also been found to be effective catalysts for oxidative or reductive chemical conversions.

The catalysts act on oxygen in the presence of methane forming aldehydes, other partially oxidized carbon products and water. Methane or natural gas is catalytically oxidized to formaldehyde under conditions of higher temperature and modest pressure. For example methane is catalytically oxidized to formaldehyde using a cobalt (II) oxalate catalyst on a silica alumina support in a temperature range of 350° C. to 400° C. while ethane is catalytically converted to acetaldehyde and other products under similar conditions.

The process for catalytic reduction of polar organic compounds such as alcohols, aldehydes, aldols and other carbon compounds using methane, natural gas or other gaseous hydrocarbons is a general process designed to replace hydrogen in production of condensable hydrocarbons. The process is based on catalysts possessing multiple metal type transition metal compounds, such as [iron]₂ or [manganese]₂ type compounds and numerous others in conjunction with non-fluorinated magnesium halide promoter. Different first row transition metal catalysts have been prepared for conversion of methane to condensable organic compounds at modest pressures and at temperatures of 350° C. to 400° C. Reaction pressures of 0 to 60 psi have been employed in several of the catalytic methane conversion processes, although higher pressures are also effective. This process may also be employed for reduction of carbon oxides forming hydrocarbons.

Catalyst Selection Considerations

The fundamentals of catalysis effort forms a basis for selecting molecular catalysts for specified chemical reactions through computational methods by means of the following six procedural steps. An acceptable methanation mechanism, involving a pair of metal atoms, was established for methane gas in the presence of oxygen or a polar reactant (step 1). A specific transition metal, such as cobalt, was selected as a possible catalytic site as found in an M-M or Co-Co string (step 2), bonded with oxygen or sets of polar organic molecules in symmetric configurations, and having a computed bonding energy to the associated polar reactants of less than −60 kcal/mol (step 3). The first valence state for which the energy values were two-fold degenerate was 2+(step 4). Acetate, chloride and other anions may be chosen provided they are chemically compatible with the metal, M (Co), in formation of the catalyst (step 5). A test should also be conducted to establish compliance with the rule of 18 (or 32) to stabilize the catalyst so compatible ligands may be added to complete the coordination shell (step 6). This same process may be applied for selection of a catalyst using any of the first, second or third row transition metals, however, only those with acceptable low positive or negative bonding energies can produce effective catalysts. Approximate, computed, relative bonding energy values may be computed using a semi-empirical or other algorithm. This computational method indicated that several of the first row transition metal complexes can produce usable catalysts once the outer coordination shell has been completed with ligands. Second row and third row transition metal complexes were also indicated to produce active catalysts.

Transition metal catalysts loaded onto silica, silica-alumina, alumina or other support materials have been employed. Non-fluorinated magnesium halide compounds combined with and/or loaded onto the catalyst support are effective promoters of the catalytic process. Addition of 0.01 to 90 percent of a catalyst and a balance of non-fluorinated magnesium halide salts promotes methanation reduction reactions.

Description of Catalyst Preparation

Catalyst preparation has been conducted using nitrogen saturated solvents and nitrogen blanketing to minimize or eliminate air oxidation of the transition metal compounds during preparation. Transition metal catalysts, effective for conversion of methane, natural gas and other carbon based compounds to condensable organic compounds, can be produced by combining transition metal salts in their lowest standard oxidation states. Thus, such transition metal catalysts can be made by mixing transition metal (I or II) chlorides with sodium acetate or ammonium hydrogen oxalate in a 1 to 2 or 1 to 3 ratio, or by forming transition metal compounds in a reduced state by similar means where di-, tri- and/or poly-metal compounds result.

EXAMPLE 1

The cobalt acetate catalyst may be prepared in a nitrogen atmosphere by addition of 0.15 gram (2 mmol) of ammonium acetate to 0.25 gram (1 mmol) of light pink colored cobalt (II) acetate tetrahydrate dispersed in 15 grams of nitrogen purged ethanol with mixing and gentle heating. To the resulting deep magenta to purple solution was added to 20 grams of a silica alumina support and the mixture was dried under nitrogen producing the catalyst.

EXAMPLE 2

Preparation of manganese oxalate catalyst may be conducted in a nitrogen atmosphere by addition of 0.28 gram (2 mmol) of ammonium oxalate to 0.20 gram (1 mmol) of manganese (II) chloride tetrahydrate dissolved in 10 grams of nitrogen purged water with mixing. To the resulting solution was added 20 grams of silica alumina support and the mixture was dried under nitrogen producing the catalyst.

Catalytic Conversion of Methane to Condensable Hydrocarbons

The solid cobalt catalyst of example 1 (˜20 grams) was mixed with approximately 2 grams of magnesium chloride and loaded into a one half inch diameter stainless steel reactor tube fit with reactant inlet, pressure and temperature monitoring, product outlet and a means of controlling methane flow rate. In addition, a means of dehydration of the reaction stream was applied. The reactor was flushed with methane and heated to 350° C. to start the reaction. Air addition rates of 0.15 to 0.25 mole per minute at 15 psi in combination with 0.40 to 0.75 mole of methane at 30 psi produced a gas stream of approximately 45 psi flowing through the reactor. Products formed were immediately measured for formaldehyde and condensable hydrocarbons to confirm there formation. This process was repeated several times for temperatures in the range of 330° C. to 450° C. and pressures in the range of 30 to 60 psi. 

1. A rapid (less than 30 minutes) process for catalytic oxidative chemical conversion of gaseous reactants comprising methane, natural gas or other gaseous hydrocarbons combined with air, oxygen or polar reactants to products and catalytic methanation of resulting oxidized products comprising alcohols, aldehydes, ketones, glycol ethers and carbon oxides to condensable hydrocarbons using reactants comprising methane, natural gas or other gaseous hydrocarbon reducing agents, where no hydrogen gas, strong oxidizing agents or electromagnetic energy of any type were employed, catalysts being made from di-metal, tri-metal and/or poly-metal backbone or molecular string type compounds of transition metals, comprising titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zirconium, niobium, molybdenum, ruthenium, rhodium, palladium, silver, hafnium, tantalum, tungsten, rhenium, osmium, iridium, platinum, gold and combinations thereof in conjunction with a non-fluoride promoter comprising magnesium chloride, bromide or iodide.
 2. A rapid (less than 30 minutes) process for catalytic oxidative chemical conversion of gaseous reactants comprising methane, natural gas or other gaseous hydrocarbons combined with air, oxygen or polar reactants to products and catalytic methanation of resulting oxidized products comprising alcohols, aldehydes, ketones, glycol ethers and carbon oxides to condensable hydrocarbons using reactants comprising methane, natural gas or other gaseous hydrocarbon reducing agents, where no hydrogen gas, strong oxidizing agents or electromagnetic energy of any type were employed, catalysts being made from di-metal, tri-metal and/or poly-metal backbone or molecular string type compounds of transition metals, comprising titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zirconium, niobium, molybdenum, ruthenium, rhodium, palladium, silver, hafnium, tantalum, tungsten, rhenium, osmium, iridium, platinum, gold and combinations thereof in conjunction with a non-fluoride promoter comprising magnesium chloride, bromide or iodide at temperatures between 330° C. and 450° C.
 3. A rapid (less than 30 minutes) process for catalytic oxidative chemical conversion of gaseous reactants comprising methane, natural gas or other gaseous hydrocarbons combined with air, oxygen or polar reactants to products and catalytic methanation of resulting oxidized products comprising alcohols, aldehydes, ketones, glycol ethers and carbon oxides to condensable hydrocarbons using reactants comprising methane, natural gas or other gaseous hydrocarbon reducing agents, where no hydrogen gas, strong oxidizing agents or electromagnetic energy of any type were employed, catalysts being made from di-metal, tri-metal and/or poly-metal backbone or molecular string type compounds of transition metals, comprising titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zirconium, niobium, molybdenum, ruthenium, rhodium, palladium, silver, hafnium, tantalum, tungsten, rhenium, osmium, iridium, platinum, gold and combinations thereof in conjunction with a non-fluoride promoter comprising magnesium chloride, bromide or iodide at temperatures between 330° C. and 450° C., and pressures of less than 20 atmospheres.
 4. A rapid (less than 30 minutes) process for catalytic oxidative chemical conversion of gaseous reactants comprising methane, natural gas or other gaseous hydrocarbons combined with air, oxygen or polar reactants to products and catalytic methanation of resulting oxidized products comprising alcohols, aldehydes, ketones, glycol ethers and carbon oxides to condensable hydrocarbons using reactants comprising methane, natural gas or other gaseous hydrocarbon reducing agents catalysts being made from di-metal, tri-metal and/or poly-metal backbone or molecular string type compounds of transition metals, comprising titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zirconium, niobium, molybdenum, ruthenium, rhodium, palladium, silver, hafnium, tantalum, tungsten, rhenium, osmium, iridium, platinum, gold and combinations thereof in conjunction with a non-fluoride promoter comprising magnesium chloride, bromide or iodide.
 5. A rapid (less than 30 minutes) process for catalytic oxidative chemical conversion of gaseous reactants comprising methane, natural gas or other gaseous hydrocarbons combined with air, oxygen or polar reactants to products and catalytic methanation of resulting oxidized products comprising alcohols, aldehydes, ketones, glycol ethers and carbon oxides to condensable hydrocarbons using reactants comprising methane, natural gas or other gaseous hydrocarbon reducing agents catalysts being made from di-metal, tri-metal and/or poly-metal backbone or molecular string type compounds of transition metals, comprising titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zirconium, niobium, molybdenum, ruthenium, rhodium, palladium, silver, hafnium, tantalum, tungsten, rhenium, osmium, iridium, platinum, gold and combinations thereof in conjunction with a non-fluoride promoter comprising magnesium chloride, bromide or iodide at temperatures between 330° C. and 450° C.
 6. A rapid (less than 30 minutes) process for catalytic oxidative chemical conversion of gaseous reactants comprising methane, natural gas or other gaseous hydrocarbons combined with air, oxygen or polar reactants to products and catalytic methanation of resulting oxidized products comprising alcohols, aldehydes, ketones, glycol ethers and carbon oxides to condensable hydrocarbons using reactants comprising methane, natural gas or other gaseous hydrocarbon reducing agents catalysts being made from di-metal, tri-metal and/or poly-metal backbone or molecular string type compounds of transition metals, comprising titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zirconium, niobium, molybdenum, ruthenium, rhodium, palladium, silver, hafnium, tantalum, tungsten, rhenium, osmium, iridium, platinum, gold and combinations thereof in conjunction with a non-fluoride promoter comprising magnesium chloride, bromide or iodide at temperatures between 330° C. and 450° C., and pressures of less than 20 atmospheres.
 7. A process for catalytic oxidative chemical conversion of gaseous reactants comprising methane, natural gas or other gaseous hydrocarbons combined with air or oxygen to products and catalytic methanation of resulting oxidized products comprising alcohols, aldehydes, ketones, glycol ethers and carbon oxides to condensable hydrocarbons using reactants comprising methane, natural gas or other gaseous hydrocarbon reducing agents catalysts being made from di-metal, tri-metal and/or poly-metal backbone or molecular string type compounds of transition metals, comprising titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zirconium, niobium, molybdenum, ruthenium, rhodium, palladium, silver, hafnium, tantalum, tungsten, rhenium, osmium, iridium, platinum, gold and combinations thereof in conjunction with a non-fluoride promoter comprising magnesium chloride, bromide or iodide.
 8. A process for catalytic oxidative chemical conversion of gaseous reactants comprising methane, natural gas or other gaseous hydrocarbons combined with air or oxygen to products and catalytic methanation of resulting oxidized products comprising alcohols, aldehydes, ketones, glycol ethers and carbon oxides to condensable hydrocarbons using reactants comprising methane, natural gas or other gaseous hydrocarbon reducing agents catalysts being made from di-metal, tri-metal and/or poly-metal backbone or molecular string type compounds of transition metals, comprising titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zirconium, niobium, molybdenum, ruthenium, rhodium, palladium, silver, hafnium, tantalum, tungsten, rhenium, osmium, iridium, platinum, gold and combinations thereof in conjunction with a non-fluoride promoter comprising magnesium chloride, bromide or iodide at temperatures between 330° C. and 450° C.
 9. A process for catalytic oxidative chemical conversion of gaseous reactants comprising methane, natural gas or other gaseous hydrocarbons combined with air or oxygen to products and catalytic methanation of resulting oxidized products comprising alcohols, aldehydes, ketones, glycol ethers and carbon oxides to condensable hydrocarbons using reactants comprising methane, natural gas or other gaseous hydrocarbon reducing agents catalysts being made from di-metal, tri-metal and/or poly-metal backbone or molecular string type compounds of transition metals, comprising titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zirconium, niobium, molybdenum, ruthenium, rhodium, palladium, silver, hafnium, tantalum, tungsten, rhenium, osmium, iridium, platinum, gold and combinations thereof in conjunction with a non-fluoride promoter comprising magnesium chloride, bromide or iodide at temperatures between 330° C. and 450° C., and pressures of less than 20 atmospheres.
 10. A process for catalytic chemical conversion of gaseous reactants comprising methane, natural gas or other gaseous hydrocarbons combined with air or oxygen to products comprising condensable hydrocarbons using catalysts made from di-metal, tri-metal and/or poly-metal backbone or molecular string type compounds of transition metals, comprising titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zirconium, niobium, molybdenum, ruthenium, rhodium, palladium, silver, hafnium, tantalum, tungsten, rhenium, osmium, iridium, platinum, gold and combinations thereof in conjunction with a non-fluoride promoter comprising magnesium chloride, bromide or iodide.
 11. A process for catalytic chemical conversion of gaseous reactants comprising methane, natural gas or other gaseous hydrocarbons combined with air or oxygen to products comprising condensable hydrocarbons using catalysts made from di-metal, tri-metal and/or poly-metal backbone or molecular string type compounds of transition metals, comprising titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zirconium, niobium, molybdenum, ruthenium, rhodium, palladium, silver, hafnium, tantalum, tungsten, rhenium, osmium, iridium, platinum, gold and combinations thereof in conjunction with a non-fluoride promoter comprising magnesium chloride, bromide or iodide at temperatures between 330° C. and 450° C.
 12. A process for catalytic chemical conversion of gaseous reactants comprising methane, natural gas or other gaseous hydrocarbons combined with air or oxygen to products comprising condensable hydrocarbons using catalysts made from di-metal, tri-metal and/or poly-metal backbone or molecular string type compounds of transition metals, comprising titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zirconium, niobium, molybdenum, ruthenium, rhodium, palladium, silver, hafnium, tantalum, tungsten, rhenium, osmium, iridium, platinum, gold and combinations thereof in conjunction with a non-fluoride promoter comprising magnesium chloride, bromide or iodide at temperatures between 330° C. and 450° C., and pressures of less than 20 atmospheres. 